Turbochargers are well known devices for supplying air to the intake of an internal combustion engine at pressures above atmospheric (boost pressures). A conventional turbocharger essentially comprises an exhaust gas driven turbine wheel mounted on a rotatable shaft within a turbine housing. Rotation of the turbine wheel rotates a compressor wheel mounted on the other end of the shaft within a compressor housing. The compressor wheel delivers compressed air to the intake manifold of the engine, thereby increasing engine power.
The turbocharger shaft is conventionally supported by journal and thrust bearings, including appropriate lubricating systems, located within a central bearing housing connected between the turbine and compressor wheel housing. It is well known that providing an effective sealing system to prevent oil leakage from the central bearing housing into the turbine housing is problematic. It is however important to prevent oil leaking into the turbine housing where it will mix with the exhaust gas and increase exhaust emissions any may cause damage to downstream components such as a catalytic converter.
A turbocharger turbine wheel may be friction welded to a seal boss at the end of the turbocharger shaft, the seal boss having a larger diameter than the shaft and rotating within an annular passage through a housing wall separating the bearing housing from the turbine housing. Known oil seal arrangements comprise a seal ring located around the seal boss within the passage providing a seal in the manner of a piston ring.
Whereas the turbine of a turbocharger drives a compressor, in a power turbine the end of the turbine shaft remote from the turbine wheel transmits power via a mechanical coupling. In a turbocompound engine comprising a power turbine connected in series with the turbine of a turbocharger, a gear wheel may be fixed to the end of the power turbine shaft to transmit power into the crankshaft of the engine via an appropriate coupling (such as for example a fluid coupling or a gear or other drive mechanism), hydraulically, mechanically or electrically. As with a turbocharger, the shaft of a power turbine is supported on bearing assemblies, including appropriate lubricating systems, located within a bearing housing connected to the turbine housing. The bearing arrangement at the turbine end of the shaft may be substantially the same as that found in a turbocharger, although the bearing arrangement at the drive end of the shaft may be a ball bearing assembly.
Turbines, whether included in a turbocharger, a power turbine or other turbomachine, are generally provided with a heat shield located between the turbine wheel and the turbine/bearing housing wall through which the turbine shaft passes. The heat shield, which is typically a sheet metal component installed in the turbine housing behind the turbine wheel, is provided to prevent overheating of the bearing housing, which can for instance result in oil coking in the bearing housing.